CHAPTER VI. 

 DARWIN'S EXPLANATION OF EVOLUTION. 



Summary of the Evidence. 



WE have now considered the chief sources of 

 direct evidence which have been brought forward in 

 favor of organic evolution, as the result of many 

 years' investigation. It remains to consider the 

 various scientific theories which have been advanced 

 to explain evolution. Before proceeding to this 

 subject, it will be well to notice what has been 

 proved by the evidence already deduced, and what 

 inferences can be legitimately drawn. It will in the 

 first place be acknowledged that nothing has been 

 positively proved as to the question at issue, for 

 from its very nature evolution is beyond proof. 

 But while no demonstration is possible, the evidence 

 gradually accumulated has seemed so strong to 

 scientists that it has led to an almost universal 

 acceptance of evolution in some form. We have 

 seen that the amount of variation possible in any 

 species is undoubtedly very great, and, so far as can 

 be discovered, it is practically unlimited ; that 

 species and varieties merge into each other in such 

 a way as to be undistinguishable ; that the only 

 definition ever given of a species breaks down, since 

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